Simplify multi-agent mode controls

[jif-oai]

Why

Multi-agent delegation policy was split across multiAgentMode, features.multi_agent_mode, and usage_hint_enabled. These controls could disagree: a requested mode could be downgraded by the feature flag, and disabling usage hints also disabled mode instructions.

Some clients also need multi-agent tools without adding delegation-policy text to model context. The previous two-mode API could not express that directly.

What changed

multiAgentMode is now the only live delegation-policy control:

Mode	Behavior
none	Keep multi-agent tools available without adding mode instructions.
explicitRequestOnly	Only delegate after an explicit user request.
proactive	Delegate when parallel work materially improves speed or quality.

• new threads default to explicitRequestOnly; omitting the mode on later turns keeps the current value
• thread start, resume, fork, and settings responses always report the concrete current mode instead of null
• mode selection remains sticky across turns and resume
• usage-hint text no longer controls whether mode instructions apply
• features.multi_agent_mode and usage_hint_enabled remain accepted as ignored compatibility settings so existing configs continue to load
• app-server documentation and generated schemas describe the three-mode API

Tests

• just test -p codex-core multi_agent_mode
• just test -p codex-core multi_agent_v2_config_from_feature_table
• just test -p codex-core spawn_agent_description
• just test -p codex-features
• just test -p codex-app-server-protocol
• just test -p codex-app-server multi_agent_mode

[chatgpt-codex-connector]

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[jif-oai]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 433c03a72c

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".